TEMPERATURE COMPENSATED CURRENT MEASUREMENT

• US 20150015244A1
• Filed: 02/01/2013
• Published: 01/15/2015
• Est. Priority Date: 02/03/2012
• Status: Active Grant

• Current Assignee: Power Electronic Measurements Ltd
• Original Assignee: Power Electronic Measurements Ltd
• Inventors: Ray, William Frederick, Hewson, Christopher Rene, Aberdeen, Joanne Marie
• Granted Patent: US 9,970,963 B2
• Time in Patent Office: Days
• US Class Current: 324/127
• CPC Class Codes: G01R 15/181 using coils without a magnetic core, e.g. Rogowski coils
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 19/32 Compensating for temperature change

Abstract

A temperature compensated current measurement device comprises a Rogowski coil having a terminating impedance arranged to adjust the attenuation of the coil to balance changes in coil sensitivity so that the output voltage indicative of measured current remains substantially unchanged, the terminating impedance having different values above and below a threshold frequency.

Claims

1. A current measuring device comprising a conductive coil, said conductive coil being arranged to produce a voltage as a result of a current being measured by the current measuring device, said conductive coil having a temperature-dependent coil sensitivity factor associated therewith;

the device further comprising a terminating impedance connected to the conductive coil, said terminating impedance being arranged to attenuate the voltage produced by the conductive coil by a temperature-dependent attenuation factor and to connect the conductive coil to an output;

said output being arranged to produce an output indicative of the current being measured;

wherein the terminating impedance is arranged so that, when there is a temperature change in the conductive coil which causes a corresponding change in the coil sensitivity factor, the attenuation factor also changes so that a value of the output voltage remains substantially unchanged, and the terminating impedance has a first impedance value below a predetermined threshold frequency for the output and a second, different impedance value above said predetermined threshold frequency.

2. A current measuring device as claimed in claim 1 wherein the conductive coil comprises a Rogowski coil.

3. A current measuring device as claimed in claim 2 wherein the Rogowski coil comprises any of:

a clip-around coil, a closed-loop coil, a printed circuit Rogowski coil and a coil wound on a non-conductive former.

4. A current measuring device as claimed in claim 1 wherein the output includes an integrator.

5. A current measuring device as claimed in claim 1 wherein the terminating impedance comprises a resistor.

6. A current measuring device as claimed in claim 1 wherein, in operation, the terminating impedance behaves like a resistor at least over a predetermined frequency range.

7. A current measuring device as claimed in claim 1 wherein said predetermined frequency threshold is greater than a range of frequencies for the measured current but lower than a natural frequency of the conductive coil.

8. A current measuring device as claimed in claim 1 wherein one of said first and second impedance values is determined so that, when the terminating impedance takes on said value, it provides a damping effect on the conductive coil.

9. A current measuring device as claimed in claim 1 wherein the conductive coil has an associated coil resistance wherein the value of the coil resistance is less than a value of the terminating impedance at least over part of an operational frequency range of the current measuring device.

10. A current measuring device as claimed in claim 9 wherein a value of the coil resistance associated with the conductive coil is temperature dependent.

11. A current measuring device as claimed in claim 1 wherein the terminating impedance comprises a resistor or a capacitor.

12. A method of measuring a current, comprising:

using the current measuring device as claimed in claim 1 to measure the current.

13. (canceled)